OSPF Part 1

so OSPF OSPF stands for open open shortest path first open shortest path first that's the meaning of OSPF open shortest path first open shortest path first the reason why this is called open shortest path first is there is an algorithm called Dijkstra algorithm this Dijkstra algorithm is has got a name after a man called Dijkstra then if there was a man called Dijkstra who designed an algorithm called shortest path first it is in an algorithm called a SPF shortest path first now based on this shortest path first algorithm this routing protocol is designed using this algorithm the routing protocol is designed Dijkstra did not design any routing protocol he just design an algorithm so based on this algorithm OSPF the routing protocol OSPF is made this is a routing protocol that we learn we are not learning algorithm we are learning the protocol that is designed developed using SPF algorithm and this SPF algorithm though it is designed by Dijkstra it is made as open standard okay so this shortest path first algorithm design by Dijkstra has made open standard by Dijkstra open standard what is meant by open standard it is open to use it it is not owned by someone it is open to use anyone can use it that's what Dijkstra made it fixed after designing the algorithm he made it as open no need to write a letter to Dexter and ask permission to use this you're open to use it Dijkstra's algorithm so because this routing protocol is designed using developed using this open protocol you got the name open shortest path first OSPF is the open shortest path first because this protocol is an open open standard OSPF is an open standard now you can see this protocol all over the world widely used than any other protocol this protocol is widely used all over the world this is the world this is one of the main reason it's not proprietary it is open standard it is open for anyone to use this protocol is open this protocol has become open because it was developed using open algorithm open standard algorithm though it is designed by Dickson Wright has he has made it open standard now this routing protocol OSPF is what we are trying to learn we are not trying to learn the algorithm SPF that we if you give three routes this algorithm can easily find out the shortest route but giving three route to the algorithm is taken care by the routing protocol I'm just giving example three route multiple routes you in network a network there are there are multiple routes to reach some destination the routing protocols will discover all the paths and give that gives us path information to SPF algorithm SPF algorithm will run on it and find the shortest path and give the answer things like in colleges you might have learnt binary tree algorithm now if you see here in order to go to this X you can come like this you can also come like this there are two ways what does SPF algorithm binary tree algorithm will do it will pick this root Y let's say on each thing you have you have a cost of ten ten ten ten ten ten ten what binary tree will do it will add this ten and ten you get only 20 but if you come like this it is 10 plus 10 plus 10 30 which is shortest this is shortest so OSPF will pick this path as the best path to reach the destination X so SPF algorithm will find the shortest path like this but for a spear Felger rhythm to find the shortest path every router should know all the links in the topology see this is one complete apology if this router wants to go here if it wants to go to this network if this wants to go to here this router should know the complete apology only then it will find the shortest path every router needs to know the complete picture of the topology likewise likewise OSPF what it does is in order to learn the complete apology all the routers that is enabled with OSPF will send link state advertisement they said link stood advertisement what is link stood advertisement the advertisement about the link that they have directly connected and the bandwidth on them subnet on them IP address on them all this information they send them they don't send the routing table periodically like Ripon eigrp but they sell only the link status just the link status old router will send just the link status link state advertisement they send the link status to all other routers now based on the link state did the link state advertisement every router will learn this topology every router we learn in their in their memory in their imagination they will know that I'm here and I'm connected to two more routers and that two more disconnected down here and we are all connected like this this this picture will be there with everyone in their memory they learn the route they learn the topology how they learn the topology and the help of link-state advertisements this topology is called as link state database unless DB link state database in EIGRP also we learned three tables routing table neighbor table and topology table likewise you know SPF also you have routing table topology table and neighbor table topology table we call it as database link state database routing table will have the best routes how the best route for a destination is found by running an SPF algorithm on it the best route will be installed in the routing table the other possible routes will not be seen in the routing team it will be seen only in the database and the third table is neighbor table it will show the directly connected neighbors for this router this is directly connected so this router will have two neighbors let's say here 10.0.0.0 dot zero dot one 10.0.0.0 0 dot 0 dot 2 now router this router will have two neighbors when they stand out 0.02 and 20.00 not two but if there will be some other router ID we will talk about ready let's say this router Sauter ID is router ID is who taught you not to run to and this router is allow tri-d is sprayed at 3.3 and 3 so on this router who are all neighbors it is not 22 0.02 and 10.0.0.0 it is the router ID of that router 3des 3.3 up three and tora tora tora - these are the two neighbors of the top router so three tables neighbor table will show you the router idea of neighbor of directly connected neighbor notoriety of directly connected neighbor and it will show you the interface interface through which those neighbors or connected this is what you will see in the neighbor table whereas in the database we called a stop ology table in EIGRP here we called as database OSPF database link state database you can also call it as what apologetically you will find all possible routes for all destination alright next is the routing team this routing table will have the best route picked from this database with the with what algorithm the best route is faked with the SPF algorithm with the help of his paypal Gotham from this topology table best route will be picked and installed into the routing table best route given by SPF so this is what the three tables and no SPF a based on link state advertisement all these are possible so Oh SPF is called as what set of protocol is rip said distance-vector protocol what set of protocol is eigrp advanced distance-vector protocol some people also call this hybrid protocol I told you yesterday the OSPF is link state link state routing protocol link state routing protocol OSPF is a link state routing protocol it's a link state routing protocol OSPF is a link state routing protocol don't forget this link state routing protocol now like every protocol OSPF also has got metric metric and OSPF we call this cost what is metric in eigrp bandwidth and delay even though there are four or five key values bandwidth load delay reliability and MTU only two are considered what are they bandwidth end dealing we discussed this yesterday whereas in OSPF we have something called cost what is the metric of rip hop count here OSPF metric is cost what is cost what is cost we understand what is hop count when we talk about rip I metric he understood what is delay there will be delay on every interface and there will be a bandwidth on average those things in our nester what is this cost OSPF metric is cost or does this cost means what is this cost means cost means this 10 to the power of 8 divided by bandwidth on the link it will pick the bandwidth on the link and put it under a 10 to the power of 8 and whatever the answer comes that becomes a cost let me give you an example you have a router one that's gonna be 2 2 & 3 and they are connected like this let's say here you have 10 Mbps for arrow which is Ethernet is Ethernet works in the speed of 10 Mbps and you have Fast Ethernet here hundred MBBS now you go to the formula 10 Mbps on top 10 to the power of 8 10 Mbps if you convert into beats 10 Mbps if you convert into bits that is equal to 10 to the power of feet 8 zeros you will have so when you strike this the answer that you get is 1 so here the cost is 1 what about this one 10 to the power of 8 divided by 10 to the power of 7 because it is 10 Mbps 1-0 less when he converted to bits it is in Muhammad's and he converted to bits this the value and he cut this what do you get 10 as the answer so here the cost is 10 here the cost is 1 OSP will say this is the best route to reach X dot alpha dot beta dot gamma dot Delta this is the destination from from here you want to go Alpha Beta Gamma Delta so R we'll say let's go this way why because the cost is only one on top the cost is 10 - hi so OSP will pick this path but in the database you will have both the paths link state database you will have both butts alright so this is the metric of OSPF cost is equal to 10 to the power of 8 by bandwidth on the ceiling alright so that is the metric of for SPF and what type of protocol is OSPF it's the link state protocol and what is the administrative distance of this OSPF every protocol has got administrative distance for the static route administrative distance is 1 for rape 100m 24 eigrp 70 sorry VAR p 90 in eigrp it is 90 in EHR P there is also internal and external internal is 90 that is what we learned in CCNA but there is also external we will learn later when he come higher level that external AIG RP is 170 administrative distance of external eigrp is 170 internal is 90 now what is the administrative distance of OSPF it is 110 it's 110 110 right next is you know what is the meaning of administrator distance if you have multiple routing protocols in same router all routing protocol will say how to go to this network Alpha Beta Gamma Delta to this router now this router cannot obey every routing protocols decision so it decides to pick the one whose administrator distance is lower so if I have AI J up in OSPF EIGRP will be active takin the reason why he HR administrator distance is only 90 there is voiced by administrator distance is 100 M 10 to costly so that's the reason why we have we need the administrator distance it is just to decide when we have multiple source giving you the path to decide whose paths to take this numerical value is used there are three people telling you how to reach Delhi first guy says go by our east second guy says go via West whom he will believe he will believe the one who knows much about Delhi likewise here if multiple routing protocol gives path for a particular destination same destination but multiple paths one says go via ethernet is zero one says go away faster zero so which one are you going to take you need to see whose administrative distance is lower ERP is 90 OSPF is 110 so yeah here P will be effective or if you have repented OSPF whose path will be effective OSPF why OSPF is 110 he IGF is 120 lower the administrative distance more preference is given all right so next is the multicast address in OSPF OSPF uses multicast address 224 dot 0 dot 0.5 and 224 dot 0 dot 0.62 multicast address voice refuses to 24.0 dot 0.5 and to 24.0 dot 0.62 multicast address 5 & 6 what is the multicast address for read 224 dot 0 dot 0 dot 9 that is reposition to what is the multi get status of EIGRP 224 dot 0 dot 0 dot 10 whereas for voice PF we got to multicast address 224 dot 0 dot 0 dot 5 and to 24.0 dot 0.62 multicast address all right so we learned a few basic stuff let's get into another three important topics in OSPF there are three IDs one is area ID another one is a router ID another one is cross society what is this area ID see OSPF supports unlimited hop count always peer supports unlimited hub comes unlimited countless up count or his peer supports unlimited hop count because it supports unlimited hop count because it supports unlimited hop count it is very difficult to control if all the routers are in single group so what is P of dresses it follows an area approach all areas will be group like this this will be area 1 this will be area 2 this will be area 3 likewise you know you will have multiple areas so and all this area will have at least hundred router you can have not at least you can have any number of router even two router also ok but maximum it can have up to 255 255 outers so like this you know all areas will have lot of routers so if anyone from this area wants to talk to this area it is not possible to talk you know directly you need the backbone area this backbone area is called as area zero area zero is the backbone area all area must be directly connected to the backbone area always area zero is the backbone area you cannot make some other areas backbone area even if these two are connected like this no one from here can talk to here like this not possible it has to go through the backbone area only that is a wisp if is designed now this router that is connecting the two area the backbone area and the other area we call it as area border router ABR Area border router and each this router are called us into a internal router because it is internal to that area for but this is called as area border router why one interface is connected to area 0 another interference community area for then it is an ABR outer area border router because you group the routers into small small group what you will do you will do summarization here let's say here area you got ten dot 1.0.0 slash 16 and out to dot this 10.25 fire dot 0 dot 0 slash mr. Sahni APR what you do is you do summarization send only 10.0.0.0 to this guy so you get a summary session point if you don't have area you cannot do summarization you get the point where summarization can be done because you summarize the other area routers will not have big routing table so the clear subnets of this area will not be sent to others other area members other area members will have only the summary anyway you have only one exit why you need to know multiple subnets so anything starts with 10 it will send here and this will send here so you get a summarization point if you have area that's why OSPF is designed like this it's not only that if a small subnet goes down let's say 10.2 is going down in this area update will be sent to everyone inside the area but to the other area it won't go and disturb why for another area this 10.2 may not be relevant Network they don't frequently communicate that's why they are in different area all a network that will frequently communicate will be in single area the other area members rarely communicate then why you sending you unnecessarily small small update and disturb the other area so what it does is it localized localized the impact of topology change localize the impact of topology change any change happens in the area the change will be affecting only that area remember not the other area member so other area members are experiencing better process bandwidth and less advertisements all right so area is good that's why I always pay follows area now how do you know that this router belong to area three so we need an area ID that's why a tid area ID tells to which area - which area that interface belong to see if you take this router if you take this router one interface is area to the other interfaces area zero so interface wise area will change that's why I said area ID tells to which area the interface belong to that's what arrey ID job ad ID tells to which interface the interface belong to which interface the interface which into which area which area that interface belong next is the router ID router ID now let's say you have four routers this is first order second router third router fourth router let's say four outers first router is sending some updated first router is sending some update two two two is forwarding two three and three is forwarding to four and four if four words back to one it's a loop one only sent eight if one is learning again the same thing then it will become a loop it should not learn like that so to avoid that what you do is you put an ID this is sent by one sent by one sent by once in two by one now when one receives the same packet with its own ID you won't take so this one is part this one is the one which identifies who sent it that is what called is router ID so every router will pick one router ID every router will pick one router ID but that router ID will not be like one or two or three or four it will be a 32-bit address like this one dot one dot one dot one like this it will be a 32-bit address now this address can be given manually manually we can give the router ID by using the command router ID next if you don't give manually it will check whether you have a loopback interface loopback interface or logical interface that we create on the router it will pick the IP address from the loopback interface what if I have to loop back interface one dot one dot one dot one 11.11 dot 11.11 let's say this is Lubeck zero this is low back one there are two low back interface address which one it will take now there are four addresses in this router but this is Fast Ethernet one this fast and zero Schneider 0 this is not loopback so it won't take this for this these are the two loopback interface their logical interface I will show you how to create now it will pick one of this address based on what the biggest biggest address on loopback interface loopback interface it's not loopback address Lubeck interface loopback address is different you remember in the beginning we learned 127 . 1.1.1 this 127 if it starts it is not a valid IP address it's a loopback address that is not the one which we are discussing here now it's just a logical interface we create it's an interface we create logically it is not a physical port it's not a physical interface logical interface that we create to simulate some network now I create Lubeck zero and give this address so it my router shows as if it is connected to one network and 11 it all so the biggest address on the loopback interface will be picked desde route ready so Levin dot 11.11 at 11 will be taken as we now try D now manually you didn't give means it will pick the loopback interface so manually up so you didn't give loopback out so you don't have see this also you don't have then how the router ID will be picked automatically it will be picked automatically based on the interface physical interface same rule biggest address on the physical physical interface first priorities whether administrator is given manually if he has not given then if you go and pick the biggest loopback interface address if the loopback interface address is not present if there is no blue back interface she flew back interface is not present it will pick the biggest IP address from the physical interface physical interface so if there is no loopback interface what will be the router ID 20.0 type 0.1 because this biggest this is how the router ID is selected next is process ID process ID is just locally significant number you can give process ID 1 for this 2 for this 3 for this nothing wrong if you if you have the same number also nothing wrong process ID is used to identify the OSPF process running on a router is used to identify the OSPF process running on the router on the router so if you run into a spear one in one OSPF more than two sorry if you run over in one way in one router if you run in one router more than two OSPF one OSPF for this interface another OSPF for this interface how we will differentiate by seeing this number so this number is what called as process ID to differentiate one ôs fear from the other OSPF you can have multiple OSPF on a router to identify to differentiate what was fear from the other we use process ID ID ID router ID and process ID these 3 ID should remember what is the use of very ID ID ID tells which area that interface belong to and this should match area D must match must match with the neighbor area ID should match with the neighbor and outer I did you see identification to the router should not match should not match cross society can match need not to match it's your wish process ID can be anything if it matches also no problem if it doesn't match also no problem they are locally significant so these are the IDs that we have in OSPF now same topology yesterday's topology we will take I will show you how to configure OSPF in the topology you you you you you you all right this is the topology that we were having in the previous class all right so I think we have a GRP here in this topology instead of eigrp I'm going to replace it with OSPF and always PF will not do summarization by default that's very important let me write it down here Oh SPF will not do auto summarization no Auto summarization by default why why because we have area concept you do summarization only on a BF that's right alright so on this router let's see what protocol is running currently yeah GRP so let me cancel the da GRP no router AIG rp1 now router Reba I cancelled both the protocol show IP protocol you see no protocols similarly I will cancel it on all right now let's see how do you enable always beer this is how you should rainy blow SP router OSPF C process ID it can be any number in EIGRP in the same place we used to give autonomous system number and that should match with the neighbor but here this need not to match with the neighbor this is just a process ID locally significant to this router it will not be sent to other routers Network what are the networks this r3 has 30 got 0 dot 0 dot 0 you cannot hit enter like this in rip if you hate and red blood cell here you should to say wildcard mask what is well cut mask opposite of subnet mask what is the subnet mask for this 255 0 0 0 now wherever you see you have 0 you put 2 5 5 now wherever 255 was there you put 0 now so it becomes what 0.25 5.25 right not to do this is called while Cadmus and we are in CCNA so all we will have only one area area zero not multiple areas area zero so in this interface 30 we are running OSPF with the areas you know likewise 40 network 40 dot 0 dot 0 dot 0 0.25 fellow to 5 in out of every area 0 that's it Oh SPF is running let us do it on our two outer OSPF cross society network 20 dot 0 dot 0 dot 0 0.25 5.25 farad - Wi-Fi area 0 if you want to give manually it out ready you can give like this I am giving to put a 2.2 righto but it says already it has taken the processor let me do anything and cancel this OSPF and then put back because an outer ID already picked let me give that out radium look at this I have manually given the router ID if you don't give then it will try to see the loopback interface if there is no loopback interface it will pick the 30 0 - 0 1 which is biggest IP address network 30 dot 0 dot 0 dot 0 0.25 final - - out of Wi-Fi in here you see this ace r2 says I got a neighbour 40.3 see it is not saying 30.2 why the biggest type II errors between these two is 40.3 we don't have any loopback interface we didn't manually give on the router we didn't give you any manual and outer ID on router 3 so it says 40.3 is the route ready let's go to doctor 1-under outro and see I'm going to create a loopback interface interface Lubeck 0 IP address will be 100 or not one to five failure to fulfill it to fulfill it to - it's called logical interface there is no physically appearing port there logically an interface is created and network one is given now if I enable OSPF router OSPF one network 10.0.0.0 0.25 fine art of a failure to Wi-Fi area zero and network 20 voice 5 is enabled but what will be the router ID of this route router because I didn't give manually in this router it will be 1 1 1 1 4 this router let me show you see go to router 2 and check the neighbor see 1 1 1 1 is the neighbor let's see this command show IP ospf neighbor you sing now - 1 has got 1 1 1 1 SD an outer ID because I gave low back interface and route the three has got 4300 to 3 because we didn't give manually also we didn't give any Lubeck interface also so it will take the biggest IPS from the physical interface but if you go and check on router 1 show IP ospf neighbor it shows 2 2 2 2 as the router to router ID but we don't have low back interface how it comes because we gave manually by using a router ID command on router - so this is part 1 of OSPF for it hope you understood up to this level part o 4 is people will see another next class in the next class alright I want you to go through this video they enable when the once they upload it

Channel: Jayachandran

Views: 36,226

Keywords: Open Shortest Path First (Protocol)

Id: w0erInYjWUE

Length: 52min 14sec (3134 seconds)

Published: Sun Aug 03 2014